Whale hunting led many whale species close to extinction. Although the majority of the Southern whale populations are slowly recovering, the effects of climate change is still unknown. A research team in Australia studied the impact of two anthropogenic pressures – commercial whaling and projected climate change – in populations of blue whale (Balaenoptera musculus), fin whale (Balaenoptera physalus), humpback whale (Megaptera novaeangliae), Antarctic minke whale (Balaenoptera bonaerensi), and Southern right whale (Eubalaena australis) and their main prey, i.e. krill and copepods (most abundant small zooplankton) in the Antarctic Ocean. The researchers used a climate-biological coupled model entitled “Model of Intermediate Complexity for Ecosystem Assessments” (MICE) that links krill and whale population dynamics with climate drivers such as changes in ocean temperature, primary production and sea ice.

The authors included bi-directional interactions prey-predator in the model that allowed for three different alternatives:

– Model 1 associated krill dynamics with future changes in sea surface temperature and chlorophyll levels, indirectly linking climate factors with population dynamics of whales through changes in abundance of their prey and whale reproductive success;

– Model 2 included all the interactions of model 1 and added links between changes in sea ice extent and the distribution of whales;

– Model 3 simulated a comparative scenario where the climate drivers were dissociated from species dynamics, and the changes in whale and krill abundance were driven only by predation and competition among whales.

The models predicted negative impacts of climate change in krill species and all whale species, although the magnitude of the impacts on whales was different among populations. The results suggest that whales that feed in mid-latitudinal regions can be more affected by effects of climate change on prey abundance than whales that feed further south. Yet, the impact is difficult to quantify in ecological processes for krill and copepods, but it is important to mention that temperature increases may affect prey distribution and migratory patterns. The humpback whale and the Southern Right whale, that mainly feed in mid-latitudes, were the most affected due to predicted declines in krill and copepod abundance, highlighting that regions near the circumpolar current are highly vulnerable to climate change.

Despite the recover from whaling, the models predict climate-associated declines, even local extinctions until 2100, for blue, fin and southern right whale populations in the Pacific Ocean, and humpback and fin whale populations in the Atlantic/Indian Oceans. The predicted declines are a consequence of prey reduction (copepods/krill) due to increases in temperature and interspecific competition among whales. The researchers highlight the need to avoid extreme changes in temperature to keep a safe ecosystem for krill growth as well as to allow for whale recovery, especially blue and fin whales by adapting their migratory patterns to changes in sea ice and prey abundance in Antarctica.

This study highlights the need to continuously monitor whale populations to enhance their recovery through e.g. local management of krill populations. Yet, this could have limited success without immediate action to reduce greenhouse gases. Climate change can affect commercial fisheries for Antarctic krill directly taking into account the current predicted expansion of krill fisheries and projected ocean warming to a level that exceeds krill’s thermal tolerance.

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Source: Tullock, V., Plagányi, É., Brown, C., Richardson, A., Matear, R. (2019). Future recovery of baleen whales is imperiled by climate change. Glob Change Biol, 25: 1263-1281. doi: 10.1111/gcb.14573

Author: Cármen Sousa